Relay-Version: version B 2.10 5/3/83; site utzoo.UUCP
Posting-Version: version B 2.10.3 4.3bsd-beta 6/6/85; site ucbvax.BERKELEY.EDU
Path: utzoo!watmath!clyde!cbosgd!ihnp4!ucbvax!space
From: Dave-Platt%LADC@CISL-SERVICE-MULTICS.ARPA (Dave Platt)
Newsgroups: net.space
Subject: Tenth planet
Message-ID: <8512272010.AA02178@s1-b.arpa>
Date: Fri, 27-Dec-85 14:42:00 EST
Article-I.D.: s1-b.8512272010.AA02178
Posted: Fri Dec 27 14:42:00 1985
Date-Received: Sat, 28-Dec-85 06:21:50 EST
Sender: daemon@ucbvax.BERKELEY.EDU
Organization: The ARPA Internet
Lines: 59

Well, I'm working strictly from memory... but here's what I recall about
some work done on the "tenth planet" problem in the past few years...

About five years back (I think), someone did a fairly extensive analysis
of the orbits of Uranus, Neptune, and Pluto, using the best-available
estimates on the masses of these planets.  The results indicated that
there might be a tenth planet located roughly twice as far from the sun
as Pluto is, on the average;  its mass was estimated to be approx.
10 Earth-masses, and its current position was far outside of the
orbital plane of the known planets (I don't recall the figure for
certain, but I'm pretty sure it was at least 40 degrees and may have
been as much as 60 degrees).  The researcher who announced the results
of the calculations claimed to have narrowed the probable location
of the "new" planet down to a fairly small portion of the sky (10
degrees square?).

As I remember it, several observatories did an extensive
blink-comparison scan of that portion of the sky, comparing some old
file negatives with current photos... and didn't find anything.

So... several possibilities come to mind.

1- There is something in that portion of the sky, but it's too dim
   to be seen with standard optical instruments... possibly a planet
   with an *extremely* low albedo (would have to be *very* low for
   a planet with a ten-earth mass to be invisible), a black hole (where
   are the gammas?), or something small/massive/dim at a greater
   distance than was calculated (an old neutron star, or a very cold
   burnt-out dwarf star?).

2- There's nothing in that portion of the sky... the orbits of the
   outer planets are indeed being perturbed, but there's not a single
   object doing the perturbing;  instead, we're seeing the net effect
   of a large number of smaller objects, whose vector sum happens to
   point in the direction indicated by the orbital calculations.
   Perhaps there's a lot of old, cold matter (comet precursors?)
   floating around outside the orbit of Pluto;  the Oort cloud (or
   something related to it) may come in a lot closer than we had
   thought, or be much denser than previous calculations had
   indicated.

3- Something else is going on.  Possibly there's some exotic thingie
   floating around not far from our solar system... a cosmic "string",
   a dense clump of photinos or axons (sp?), or some other strange
   form of "dark matter".  Cosmologists are still trying to figure out
   how much dark matter exists in our galaxy (and in the universe), and
   what forms that dark matter takes... neutrinos with a nonzero mass,
   supersymmetric particle partners, etc. etc. and so on.  Possibly
   this dark matter occasionally forms into clumps, sufficiently
   coherent and massive to tweak the orbits of the outer gas giants in
   our solar system, but sufficiently isolated to be invisible (except
   by its gravitational interaction with our system).  Maybe the "shadow
   world" is actually out there!

Take your pick.  The jury is still out, of course... we can't yet say
that there is no tenth planet, only that we haven't unambiguously
detected the presence of one.  I rather like the third alternative;  if
it's true, it would once again bring home the realization that the
universe is stranger than we have yet imagined.